Sprockets Made of Two Materials with Half Holes on the Edge of Central Portion

ABSTRACT

The present sprocket wheel invention enhances the efficiency of the sprockets made of two materials, e.g., a lighter material at central portion of the sprocket and a hard material at peripheral portion of the sprocket comprising teeth, by drilling half holes on the outer edge of the central portion and half holes on the inner edge of the peripheral portion of the sprocket. In the preferred embodiment, half of the thickness of the sprocket is the entire hole on the peripheral portion of the sprocket with harder materials, and the other half of the thickness of the sprocket is designed to have said half holes for rivets to attach the central portion and the peripheral portion of the sprocket.

FIELD OF THE INVENTION

The invention relates to sprocket wheels, especially for those intended for outside use in power transmission of motor vehicles.

BACKGROUND OF THE INVENTION

Power transmissions by chains are widely used in various vehicles, e.g., bicycles and motorcycle. The sprockets in these chain-transmissions transmit the torque from the axels to the chain by the sprocket teeth. For high performance sprockets, two requirements are important. (i) The sprockets must sustain high torque. (ii) The sprockets must be lightweight, for the weight in vehicle would increase the burden on other part of the vehicle, e.g., the engine and the sprocket teeth.

It is not a new idea to use two different materials for the central portion and the peripheral portion of the sprockets, so that lightweight but relatively soft materials can be used at the central portion of the sprockets and harder but heavier materials can be used at the peripheral portion comprising teeth. U.S. Pat. No. 969,237, which was patented in 1910, is one of the examples.

The basic design, which is composed of a central portion and a peripheral portion comprising teeth is widely used. See also U.S. Publication No.: US 2005/0272546.

In certain applications of the two-material design, e.g., U.S. Pat. No. 7,481,729, as well as U.S. Pat. No. 969,237, the peripheral portion's perforated inward extensions, i.e., the toothed portion, that overlap with the central portion with corresponding recesses and holes, act as connection between the central portion and the peripheral portion of the sprocket. That design creates (i) the weak point in the design, i.e., the necks of the extensions, and (ii) the compromise between the strength of the connection and the weight, i.e., the increased number of extensions increases the connective strength but also increases the weight of the sprocket, while the decreased number of extensions increases the force on each extension and thereby increases the metal fatigue at the necks of the extensions.

As the weight of the material increases proportional to the square of the diameter, the thickness of the peripheral portion, i.e., the portion of the diameter that is occupied by the peripheral portion, which is at the outer limit of the sprocket, is critically related to the weight of the overall sprocket. A slight increase in the thickness of the peripheral portion would increase the weight of the entire sprocket significantly.

SUMMARY OF THE INVENTION

The present invention is used in the design of sprocket by using two materials, a lighter material for the central portion and a harder material for the peripheral portion. By providing a novel means to attach the central portion of a sprocket to the peripheral portion, the invention allows the increased area of the central portion of the sprocket, and eliminates the weak points in the traditional design, i.e., the neck of the extensions for the purpose of joining the two portions. In one of the embodiments, the connecting holes are drilled on the peripheral portion of the sprocket, with half holes drilled on the outer edge of the central portion of the sprocket matching the half holes drilled on the inner edge of the peripheral portion of the sprocket. This design eliminated the necessity of an extension from the peripheral portion to overlap with the central portion, so rivets could be applied to join the central portion and the peripheral portion of the sprocket, and thereby allow a flexible number of holes, i.e., rivets, to join the central portion and the peripheral portion of the sprocket at expected strengthened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the sprocket, when assembled, according the present invention.

FIG. 2 is a cross-section view of the sprocket from FIG. 1., when both portions are joined together by rivets.

FIG. 3 is a plan view of the central portion of the sprocket, according the present invention.

FIG. 4 is a cross-section view of the central portion from FIG. 3.

FIG. 5 is a plan view of the rim portion of the sprocket, according to the present invention.

FIG. 6 is a cross-section view of the peripheral portion from FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, the sprocket is made of two parts, i.e., the central portion (1) and the peripheral portion (2). The central portion is connected to the axel and the peripheral portion comprises teeth (3). The central and peripheral portions are joined by rivets. (See FIG. 1.) FIG. 2 is the cross-sectional view.

In the preferred embodiment, holes (4) are drilled on the inner side of the peripheral portion (2). (See FIG. 5.) Material of half of the thickness on the inner side (5) of the peripheral portion was removed so that on said half of the thickness, only halves of the holes remain. (See FIG. 6.) On the outer side of the central portion, half of the thickness on the outer side (6) of the central portion was removed so that the diameter matches that of the uncut diameter of the peripheral portion. The diameter of the uncut half of the thickness of the central portion matches the cut half of the thickness of the peripheral portion of the sprocket, with half holes drilled on the outer rim of the uncut half of the thickness of the central portion to match the half holes on the peripheral portion. (See FIGS. 3 and 4.)

Rivets (7) are used to join the central portion (1) and the peripheral portion (2) of the sprockets. (See FIGS. 1 and 2.) 

1. A sprocket comprising a. a central portion, where i. on one side of the central portion, i.e., the central removed side, material is removed for a certain thickness to a certain diameter, and, ii. on the other side of the central portion, i.e., the central unremoved side, material is not removed, allowing half holes to be drilled, and b. a peripheral portion, holes are drilled so that, i. on one side of the peripheral portion, i.e., the peripheral removed side, material is removed for a thickness, so that only half holes remain, and that the diameter of the peripheral removed side matches the diameter of the central unremoved side, with the half holes on the inner side of the peripheral portion matching the half holes on the outer rim of the central unremoved side, and, ii. on the other side of the central portion, i.e., the peripheral unremoved side, material is not removed, and the diameter of the peripheral unremoved side matches the diameter of the central removed side. c. rivets are used to fasten the central portion and the peripheral portion.
 2. The sprocket of claim 1 where the central portion and the peripheral portion are of equal thickness and the thickness of the central removed side is equal to the thickness of the central unremoved side and the thickness of the peripheral removed side is equal to the thickness of the peripheral unremoved side.
 3. The sprocket of claim 1 where the thickness of the central removed side is zero and the thickness of the peripheral unremoved side is zero. 